Biology subjects

Sadun, A. A.

Publications and source records attributed to Sadun, A. A..

4 recordsLinked to original sources

bioRxiv2026

Synergistic retinal UCHL1 dysregulation and synaptic vulnerability reflect Alzheimer's disease severity

Synaptic failure predicts cognitive decline in Alzheimers disease (AD), yet its impact and molecular drivers in the human retina remain unclear. Leveraging the retina as an accessible central nervous system (CNS) proxy, we integrated spatially resolved histopathology of retinal cross-sections with ultrastructural, proteomic, and biochemical profiling across independent postmortem cohorts spanning normal cognition, mild cognitive impairment due to AD (MCI), and AD dementia. We uncover early, progressive degeneration of excitatory glutamatergic synapses, evidenced by losses of presynaptic vesicular glutamate transporter 1 (VGLUT1) and synaptophysin, and postsynaptic density protein 95 (PSD95) and N-methyl-D-aspartate receptor subunit 2A (NMDAR2A), accompanied by disruption of synaptic ultrastructure. Retinal synaptic loss tightly associates with local accumulation of amyloid-{beta} 42 (A{beta}42) and immature tau species, heightened oxidative stress, and upregulation of the A{beta}-binding death receptor p75 neurotrophin receptor (p75NTR). Notably, the synapse-enriched deubiquitinase ubiquitin C-terminal hydrolase L1 (UCHL1) is profoundly dysregulated, correlates with synaptic integrity and cognition, and emerges as the strongest retinal predictor of Braak stage and cognitive status in multivariable machine-learning models. Together, these findings position retinal A{beta}/p75NTR-mediated UCHL1 imbalance as a proteostasis-synapse mechanistic hub and candidate biomarker reflecting AD severity.

neuroscience↗

bioRxiv2026

Molecular Mechanism of Mitochondrial Complex I Disruption by m.14484T>C Underlying Leber Hereditary Optic Neuropathy

Lebers Hereditary Optic Neuropathy (LHON) is a rare genetic condition and severe neurological disorder characterized by dysfunctional mitochondria under extreme oxidative stress, resulting in retinal ganglion cell death and subsequent rapid bilateral loss of central vision. The m.14484T>C mutation in the ND6 subunit of mitochondrial complex I is known for inducing LHON, and is a prevalent LHON-associated mutation, yet its mechanism of impairment at the molecular level is currently unresolved. In this study, we explore the biophysical underpinnings of this mutation and its role in LHON through disruption of human complex I function. We consider, using atomistic simulations, the differential thermodynamics and kinetics of coenzyme Q10 binding between the mutant and wild-type forms, altered dynamics of the complex upon mutation, and key interactions between coenzyme Q10 and complex I binding sites. The hydrogen bond network present near and within the coenzyme Q10 binding domain, along with proper hydration of E-channel residues that couple redox chemistry to proton pumping, is found to be critical for complex I stability and quinone binding, which the ND6-centered mutation disrupts. SignificanceSingle missense mutations to mitochondrial complex I can cause Leber Hereditary Optic Neuropathy (LHON), characterized by rapid loss of vision. However, the molecular defects produced by these mutations remain unclear, and largely inaccessible to experimental approaches. Using atomistic molecular dynamics simulations and analysis of quinone binding, we unveil the mechanism of the LHON mutation m.14484T>C in the ND6 subunit of human complex I. The mutation selectively disrupts the oxidized quinone state by increasing its distance from the terminal electron donor N2, and altering dynamic and hydration networks linked to proton pumping. This approach results in a redox-dependent model that explains experimentally observed changes in membrane potential and reactive oxygen species production upon disease-causing complex I mutations.

biophysics↗

bioRxiv2024

Retinal ganglion cell vulnerability to pathogenic tau in Alzheimer's disease

Accumulation of pathological tau isoforms, especially hyperphosphorylated tau at serine 396 (pS396-tau) and tau oligomers, has been demonstrated in the retinas of patients with mild cognitive impairment (MCI) and Alzheimers disease (AD). Previous studies have noted a decrease in retinal ganglion cells (RGCs) in AD patients, but the presence and impact of pathological tau isoforms in RGCs and RGC integrity, particularly in early AD stages, have not been explored. To investigate this, we examined retinal superior temporal cross-sections from 25 patients with MCI (due to AD) or AD dementia and 16 cognitively normal (CN) controls, matched for age and gender. We utilized the RGC marker ribonucleic acid binding protein with multiple splicing (RBPMS) and Nissl staining to assess neuronal density in the ganglion cell layer (GCL). Our study found that hypertrophic RGCs containing pS396-tau and T22-positive tau oligomers were more frequently observed in MCI and AD patients compared to CN subjects. Quantitative analyses indicated a decline in RGC integrity, with 46-55% and 55-56% reductions of RBPMS+ RGCs (P<0.01) and Nissl+ GCL neurons (P<0.01-0.001), respectively, in MCI and AD patients. This decrease in RGC count was accompanied by increases in necroptotic-like morphology and the cleaved caspase-3 apoptotic marker in RGCs of AD patients. Furthermore, there was a 2.1 to 3.1-fold increase (P<0.05-0.0001) in pS396-tau-laden RGCs in MCI and AD patients, with a greater abundance observed in individuals with higher Braak stages (V-VI), more severe clinical dementia ratings (CDR=3), and lower mini-mental state examination (MMSE) scores. Strong correlations were noted between the decline in RGCs and the total amount of retinal pS396-tau and pS396-tau+ RGCs, with pS396-tau+ RGC counts correlating significantly with brain neurofibrillary tangle scores (r= 0.71, P= 0.0001), Braak stage (r= 0.65, P= 0.0009), and MMSE scores (r= -0.76, P= 0.0004). These findings suggest that retinal tauopathy, characterized by pS396-tau and oligomeric tau in hypertrophic RGCs, is associated with and may contribute to RGC degeneration in AD. Future research should validate these findings in larger cohorts and explore noninvasive retinal imaging techniques that target tau pathology in RGCs to improve AD detection and monitor disease progression.

pathology↗

bioRxiv2020

Melanopsin retinal ganglion cell-driven contribution to visual and cognitive brain responses in LHON

Melanopsin retinal ganglion cells (mRGCs) are intrinsically photosensitive photoreceptors contributing to visual and non-image-forming functions of the eye. Isolating mRGC roles in humans is challenging, therefore mRGCs functions remains to be fully characterized. We explored mRGCs contribution to light-driven visual and cognitive brain responses in Lebers Hereditary Optic Neuropathy (LHON), given mRGC relative sparing in LHON. Twelve patients and twelve matched healthy controls (HC) participated in an fMRI protocol including visual and visual-cognitive paradigms under blue (480nm) and red light (620nm). Higher occipital activation was found in response to sustained blue vs. red stimulation in LHON vs. HC. Similarly, brain responses to the executive task were larger under blue vs. red light in LHON over lateral prefrontal cortex. These findings are in line with LHON mRGCs relative sparing and support mRGCs contribution to non-visual and visual functions in humans, with potential implication for visual rehabilitation in optic neuropathy patients.

neuroscience↗